I. Field of the Invention
The present invention relates generally to fuel pumps and, more particularly, to a method and apparatus for controlling a solenoid actuated inlet valve of a fuel pump to thereby reduce engine noise.
II. Description of Relevant Art
Direct fuel injection internal combustion engines have enjoyed increasing popularity in the automotive industry. Such direct injection internal combustion engines enjoy improved fuel economy and engine performance as contrasted with other types of automotive internal combustion engines.
In a direct fuel injection internal combustion engine, the fuel injector is open directly to the internal combustion chamber of the engine rather than upstream from the air intake valves. As such, the direct fuel injection internal combustion engine must generate relatively high fuel injection pressures in order to overcome the high pressures present in the internal combustion chamber during the fuel injection into the combustion chamber.
With reference to FIG. 1, a conventional prior art fuel delivery system for an automotive engine, such as a direct injection engine, is illustrated diagrammatically. The fuel delivery system 20 includes a fuel pump 22 having a fuel pressurization chamber 24. A piston 26 is reciprocally mounted within the chamber 24 and is reciprocally driven by a cam 28 which is rotatably driven in synchronism with the engine output shaft (not shown).
A fuel tank 30 provides fuel to the pressurization chamber 24 through an inlet valve 32. A solenoid 34 is mechanically coupled with the inlet valve 32 and, when energized, moves the valve to an open position and, conversely, moves the valve 32 to a closed position when de-energized. A valve control circuit 33, which preferably includes a programmed processor, controls the energization of the solenoid 34 through a solenoid connector 35.
During the downward stroke of the piston 26 and with the inlet valve 32 in an open position, the piston 26 inducts fuel through the valve 32 and into the chamber 24. Conversely, during the upward travel of the piston 26 and with the valve 32 in a closed position, the piston 26 pumps fuel from the pump chamber 24, through a one way outlet valve 36, and into a fuel rail 38.
FIG. 2 is a timing diagram of these previously described fuel pumps. As shown in FIG. 2, graph 40 represents the position of the piston 28 between its top dead center (TDC) and bottom dead center (BDC) positions. The actual shape of the graph 40 will vary depending upon the shape of the cam 28 (FIG. 1), but generally the graph 40 of the piston position is sinusoidal in shape.
Graph 42 represents the voltage output from the control circuit 36 to actuate the solenoid 34. As can be seen in FIG. 2, the solenoid 34 is energized in between TDC and BDC and de-energized in between BDC and TDC to maintain the rail pressure.
Graph 44 represents the position of the pump inlet valve 32 between a closed position 46 and an open position 48. Graph 44 representing the position of the inlet valve 32 does not precisely follow the actuation graph 42 for the solenoid 34 because inertia of the inlet valve 32 and a finite amount of time required to energize or de-energize the solenoid 34 retard the motion of the inlet valve 32. Consequently, the opening of the valve as illustrated at 50 is much more gradual than the step shown for graph 42. Likewise, the closing of the valve as indicated at 52 tapers gradually over a finite time period following de-energization of the solenoid 34.
Still referring to FIG. 2, graph 54 represents the pressure within the pump chamber 24. While the inlet valve 32 is open, the pressure within the pump chamber 24 remains a relatively steady and at same as feed pressure. However, during closure of the valve 32, the pressure within the fuel chamber 24 rapidly drops to a low value as shown at 56 because the closure of the valve 32 accelerate returning fuel from the pump chamber 24 into the fuel tank 30. Then after the inlet valve 32 is close, the upward stroke of the piston 26 rapidly increases the pressure within the pump chamber 24 to a high value indicated at 58.
Thereafter, the opening of the one way outlet valve 36 immediately causes a slight reduction in the pressure in the pump chamber 24 as shown in 60. However, the continued upward stroke of the piston 26 continues to increase the fuel chamber 24 pressure to a maximum value as shown at 62. The opening of one or more fuel injectors coupled with the downward stroke of the piston 26 then rapidly decreases the pump chamber 24 pressure to a low point as shown at 64 whereupon the above process is repeated.
Graph 66 represents the pressure within the fuel rail 38 as a function of time.
One disadvantage of direct injection engines is that the fuel pumps are relatively noisy, especially at low engine speeds. A significant part of this noise is attributable to the opening and closing of the inlet valve 32 and the resulting pressure swings indicated at 56 and 58. These sharp pressure variations result in pressure shock and engine noise.